It is known to collect a filter cake upon a filter drum and to treat this filter cake on the movable filter with a washing liquid. In the common filtering process of this type, the filter cake is washed with a washing liquid in a quantity, amount and composition such that the liquid traverses the filter cake and carries with it the soluble components. Consequently, the soluble components are washed through the filter cake and the filtering surface upon which the filter cake lies.
It is desirable to distribute the washing liquid uniformly over the entire surface of the filter cake so that the latter is washed as completely as possible and as uniformly as possible.
To this end it is generally known to distribute the washing liquid either by an overflow trough in the form of a fine water curtain upon the filter cake or to spray the filter cake with a liquid mist which is emitted from nozzles at relatively high pressure.
For many applications, the use of a disk filter is more desirable than the use of a drum filter. In a disk filter, the filtering surface is formed as a relatively thin disk which is rotated about an axis perpendicular to the filtering surface, the latter lying in a plane perpendicular, in turn, to the axis. Disk filters have been found to be particularly desirable when especially large filter surface areas are needed, for filters which are readily transported and wherever improved resolution is desired.
For example, disk filters, for a given filter surface area, require less space than a drum filter. However, disk filters have been found not to be practical for many applications, especially where an effective washing of the filter cake is desired. The difficulty is especially pronounced when the filter disks are disposed in vertical planes.
In disk filters having vertically oriented filter surfaces, there is always the danger, upon washing of the filter cake with a liquid, that the filter cake will fall off the filter surface. As a result, the use of a disk filter has generally been excluded whenever an intensive washing of the filter cake is necessary or desirable.